Polls have closed here and votes are being counted in a special election primary Tuesday that could help show just how much the endorsement of President Donald Trump or Senate Majority Leader Mitch McConnell really matters.

Republicans in Alabama will settle their party's primary for Attorney General Jeff Sessions' vacated seat, deciding between Sen. Luther Strange -- who was appointed in February to temporarily fill the seat through the special election and is backed by McConnell and Trump -- or two other major candidates, former state Supreme Court Chief Justice Roy Moore and US Rep. Mo Brooks.

As of 9:30 p.m. ET, Moore had 42% of the vote with 44% of precincts reporting. Strange had 31% and Brooks had 18%.

If one candidate tops 50% in what is expected to be a low-turnout affair -- and strategists involved in the race believe Moore has the best shot -- that candidate becomes the GOP nominee. If none of them win a majority, the top two Republicans advance to a late-September runoff.

On Alabama's airwaves, the candidates' ads have largely focused on the candidates' support for Trump.

"He is helping me in the Senate and is going to get the tax cuts for us. He's doing a lot of things for the people of Alabama and for the people of the United States," Trump said in the robo-call.

Given that Trump has weighed in for Strange, the race is a test of the President's influence in a state where his approval rating is still high and Trump is still broadly supported by Republicans.

"The President's endorsement says it all," Strange told CNN. "The people of Alabama want someone who will support the President's agenda. That's what I'm running on, and for him to say he wants me in Washington as a partner is a critical factor."

On the campaign trail, though, the three major candidates have all taken pains to never cross Trump -- including Monday, when none would criticize Trump's initial comments on the white supremacist rally in Charlottesville, Virginia.

McConnell doesn't get such kid-glove treatment.

Brooks and Moore have largely shied away from criticizing each other -- instead ganging up on Strange in part by latching him to McConnell.

At an open carry gun rights group's meeting at Mr. Wang's Restaurant in Homewood on Monday night, Moore complained to the crowd of "forces coming in from the north here and trying to buy your vote" -- a clear reference to ads from groups affiliated with McConnell.

Speaking to reporters after the event, Moore wouldn't commit to supporting McConnell as Senate majority leader.

"I don't even know Mitch McConnell. I know what he's done, and I don't favor Mitch McConnell," Moore said. "You know, I wouldn't think I would support Mitch McConnell. I've seen him do some very negative advertising -- false advertising; attacks on candidates, myself included," he said, referring to spots aired by the National Republican Senatorial Committee and the Senate Leadership Fund super PAC.

In fact, the only time Moore would take issue with Trump is over his endorsement of Strange. He noted that Trump and McConnell are "feuding" -- a reference to Trump's criticism of the Kentucky senator on Twitter over the Senate's failure to repeal Obamacare -- and called Trump's endorsement a "bad decision."

Brooks is even less ambiguous about his position on McConnell.

He toured Alabama on a bus labeled "Drain the Swamp Express," which is adorned with a "Ditch Mitch" sign. Brooks has said repeatedly that he would vote to oust McConnell as majority leader.

He called the McConnell-aligned groups' advertising "sick on their part" and said there is "no depth to deceit and lying" to which McConnell and Strange won't go.

His support from McConnell is one potential political problem for Strange. Another, possibly larger problem, is how he got the job in the first place.

Brooks on Monday used that confluence of events to allege that Strange was "holding over the head of the governor a criminal investigation while at the same time seeking a personal gain -- a United States Senate seat -- from the governor."

At his final campaign rally in Decatur, Alabama, Brooks told a small crowd at Fredrick's Outdoor -- a tractor, mower and boat retailer and repair shop -- that he needed huge turnout from the northern one-third of Alabama, which he has represented in Congress.

He also admitted in an interview that his inability to keep up financially has been a handicap.

"Luther Strange and Mitch McConnell and K Street lobbyists and special interest groups -- what we call the swamp -- are spending $5 to $10 million in attack ads that are false and deceptive and slanderous, and we don't have the money to respond to the attack ads, much less promote ourselves as we should be, or reminding voters of the corruption that surrounded the process by which Luther Strange was appointed to the United States Senate," Brooks said.

"The challenge is that I'm playing retail politics -- meeting with dozens of voters at a time, maybe hundreds -- while Luther Strange and the K Street lobbyists are defaming myself and Roy Moore, hundreds of thousands of voters at a time."

Strange, for his part, has redirected the focus of the race back to Trump -- a strategy that allows him to benefit from ads that drive wedges between the President and Strange's opponents.

"The President's endorsement says it all," Strange told CNN on Monday after an event at Salem's Diner in Birmingham. "The people of Alabama want someone who will support the President's agenda. That's what I'm running on, and for him to say he wants me in Washington as a partner is a critical factor."

The race could prove an important test headed into 2018's midterm elections. McConnell's policy is to support, through the NRSC and the Senate Leadership Fund, all incumbent Republicans. But two of those Republicans, Arizona Sen. Jeff Flake and Nevada Sen. Dean Heller, face primary challengers who will try to use the McConnell-aligned groups' spending -- and the emerging wedge between McConnell and Trump -- against the incumbents.

There are other reasons McConnell hopes to see Strange advance to a runoff -- and Moore held below 50% of the vote.

Democrats see Moore as a uniquely offensive candidate and believe his nomination could create an opening for Doug Jones, who has broad backing across the party headed into the primary, to compete in a deep-red state.

Moore is known for being stripped of his Supreme Court seat in 2003 for refusing to take down a monument of the Ten Commandments.

He was elected Alabama's chief justice again in 2013, but suspended in 2016 for refusing to enforce the US Supreme Court's ruling legalizing same-sex marriage.

His hard-line views on social issues were on display Monday night. Moore said the military needs to train "to fight wars, not for social experiments and transgenderism and feel-good stuff that's going on."